Organic anion transporting (OAT) polypeptides play an important role in the uptake of organic anions, including bile acids, bilirubin conjugates and sulfobromophthalein, in the liver (Hsiang et al., J. Biol. Chem. 274, 37161-68, 1999; Konig et al., Am. J. Physiol. Gastrointest. Liver Physiol. 278, G156-64, 2000; Kouzuki et al., J. Pharmacol. Exp. Ther. 292, 505-11, 2000). Thus, levels of organic anion transporting polypeptides can be modulated to affect the rate of drug clearance via hepatocellular uptake. Further, OATs have been found to transport eicosanoids, taurocholate, conjugated steroids, and thyroid hormones.